Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$55.62	6.781%	$59.3916	$59.39	$59.40	$59.40
Purchase #2	$191.72	13.797%	$218.1716	$218.17	$218.15	$218.20
Purchase #3	$71.48	4.610%	$74.7752	$74.78	$74.80	$74.80
Purchase #4	$97.33	6.346%	$103.5066	$103.51	$103.50	$103.50
Purchase #5	$62.72	6.530%	$66.8156	$66.82	$66.80	$66.80
Purchase #6	$90.27	4.283%	$94.1363	$94.14	$94.15	$94.10
Purchase #7	$33.86	9.143%	$36.9558	$36.96	$36.95	$37.00
7 purchase totals =	$603.00		$653.7527	$653.77	$653.75	$653.80